Oxadiazole derivatives

ABSTRACT

The present invention is concerned with certain 5-aryl or heteroaryl-1,2,4 oxadiazoles and derivatives and methods for their preparation. The compounds possess hypocholesterolemic activity.

United States Patent 1151 3,697,530 Imai et al. [45] Oct. 10, 1972 [54] OXADIAZOLE DERIVATIVES [72] Inventors: Yoshio Imai, Hyogo; Haruki Matsu- [56] References cued Osaka; Slmjim Yumgi, UNITED STATES PATENTS Kyoto; Akio Miyake, Osaka, all of Japan 3,265,692 8/1966 Harsanyi et al ..260/307 G [73] Assignee: Takeda Chemical Industries, Ltd., FOREIGN PATENTS OR APPLICATIONS Osaka Japan 1,051,322 12/1966 Great Britain ..260/307 G [22] Filed: Dec. 31, 1970 Primary Examiner-Alan L. Rotman [21] Appl' l03294 Att0rneyMilton J. Wayne I 52 vs. C]. .260/295 R, 260/247.2 R, 260/247.2 A, ABSTRACT 260/250 R, 260/256.4 R, 260/268 H, The

, present 1nvent1on 1s concerned w1th certam S-aryl 260/29367 260/295 260/307 or heteroaryl-l,2,4 oxadiazoles and derivatives and 424/248 424/ tag/ fil 6 methods for their preparation. The compounds posh h 1 t l t' 't 51 Int. Cl. ..C07d 31/34, C07d 85/52 sass ypoc 0 es em emlc ac M y [58] Field of Search ..260/295 R, 295 AM, 307 G 34 Claims, No Drawings OXADIAZOLE DERIVATIVES The present invention relates to novel oxadiazole derivatives and their pharmaceutically acceptable salts, which have effective hypocholesterolemic action.

The present invention also relates to a process for the production of these oxadiazole derivatives.

There have been many kinds of anti-arteriosclerotic agents or hypocholesterolemic agents. However, most of known hypocholesterolemic agents or anti-arteriosclerotic agents are not very satisfactory in the potency of the action, the action-mechanism, toxicity to human body, etc. Under the circumstances, the present inventors have made extensive studies for providing an effective hypocholesterolemic agent or anti-atherosclerotic agent and succeeded in synthesizing novel oxadiazole derivatives defined as below.

Further, in regard to these novel compounds, the present inventors have arrived at the following findings: these compounds have unique and strong hypocholesterolemic action, i.e. action of lowering cholesterol in living body; they have quite a low toxicity to mammals; and therefore they can be used as a safe and effective medicine for improving and/or preventing atherosclerosis.

The present invention has been accomplished on the basis .of these findings.

. Thus, the principal object of the present invention is to provide novel oxadiazole derivatives useful as a safe and effective hypocholesterolemic agent or antiatherosclerotic agent and another object is to provide a method for the production of these novel-compounds.

The oxadiazole derivatives of the present invention are those represented by the following general formula [wherein X stands for an esterified or non-esterified carboxyl group or a carboxamido group, each of R and R stands for a hydrogen atom, an aryl group or an alkyl group, and R stands for a hydrocarbon residue or a heterocyclic group, which may be substituted] and their pharmaceutically acceptable salts.

in the general formula [I], the esterified carboxyl group can be shown by the general formula XOOC- [wherein X is a hydrocarbon residue].

The hydrocarbon residue is preferably that having one to eight carbon atoms, which includes alkyl, aryl and aralkyl group. The alkyl group represented by the symbol X may be any of straight or branched chain, cyclic, saturated or unsaturated ones. The typical examples of the groups are methyl, ethyl, propyl, butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, l-propenyl, 2-propenyl, l-butenyl, 2-butenyl, and 3-butenyl. The typical examples of the aryl group are phenyl and naphthyl, and the typical ones of the aralkyl group are benzyl and phenethyl.

The carboxamido group can be shown by the general formula X"OC-(wherein X" stands for an amino or a substituted amino group). The substituted amino group represented by the symbol X" includes alkylamino, dialkylarnino, arylamino, aralkylamino or cyclic amino group, etc. The typical examples of the groups are methylamino, dimethylamino, diethylamino, 2-hydr oxyethylamino, bis(2-hydroxyethyl)amino, benzylamino, phenylamino and morpholino.

The alkyl groups represented by the symbol R and R may be any of straight or branched chain, cyclic, saturated or unsaturated ones.

The typical examples of the groups are methyl, ethyl,

propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, oxtyl, cyclopentyl, cyclohexyl, lbutenyl, 2-butenyl, 3-butenyl, l-propenyl, and 2-propenyl. Among these groups, the lower alkyl groups having one to eight carbon atoms are generally preferable. The aryl groups represented by the symbol R and R may be, for instance, phenyl, naphthyl, etc.

The hydrocarbon residue represented by the symbol R includes, for instance, alkyl, aryl and aralkyl group, etc. The alkyl groups may be any of straight or branched chain, cyclic, saturated or unsaturated ones. The typical examples of the alkyl group are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, -tertbutyl, pentyl, cyclopentyl, hexyl, cyclohexyl, cyclohexylmethyl, cyclohexylethyl, l-butenyl, 2-butenyl, 3-butenyl, l-propenyl, 2-propenyl, heptyl, octyl, monyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, oleyl, linoleyl, linolenyl.

Among these groups, the alkyl groups having five to 17 carbon atoms are preferable, and those having five to 7 carbon atoms and long straight chain ones having 15 to 17 carbon atoms are more desirable.

I The typical examples of the aryl group are phenyl, and naphthyl, and the typical ones of the aralkyl groups are benzyl and phenethyl.

The heterocyclic group represented by the symbol R includes five or six membered monocyclic ones containing one hetero atom of N, S or 0, five or six-membered monocyclic ones containing two or more, preferably two to three, hetero atoms of N, S or 0, etc.

Among these heterocyclic groups, preferable ones are those wherein a carbon atom of the heterocyclic ring links directly with the carbon atom of the S-position of the oxadiazole ring.

The typical example of these heterocyclic groups are, 2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-furyl, 3-furyl, pyrimidyl, 2-pyrazinyl, 2-morpholino, 3-morpholino, Z-piperidyl, 3-piperidyl, 4-piperidyl, 2- pyrrolidyl, 3-pyrrolidyl and Z-piperazyl.

These hydrocarbon residues or heterocyclic groups represented by the symbol R may be substituted. The substituent includes, for instance, carboxyl group, halogen atom (i.e. chlorine, bromine, fluorine, iodine), nitro group, amino group, hydroxyl group, lower alkyl group (e.g. methyl, ethyl, propyl, butyl, sec-butyl, tertbutyl, etc.), lower alkoxy group (e.g. methoxy, ethoxy, propoxy, butoxy, etc.), aryl group (e.g. phenyl, etc.), aralkyl group (e.g. benzyl, phenethyl, etc.), etc. One or more of these substituents may be attached at any optional position(s) of these hydrocarbon residues or heterocyclic groups. 7

Among the substituted hydrocarbon and substituted heterocyclic groups, most preferable and practical ones are alkyl-substituted aryls (e.g. tolyl, xylyl, butyl phenyl, etc.), halogen-substituted aryls (e.g. chlorophenyl, dichlorophenyl, etc.), N-alkyl substituted piperazyls (e.g. N-methyl-2-piperazyl, N-ethyl-Z-piperazyl, etc.), N-aralkyl substituted piperazyls (e.g. N-benzyl-2- piperazyl, etc.), nitro-substituted aryls (e.g. nitrophen, yl, etc.), amino-substituted aryls (e.g. aminophenyl,

etc.), alkoxy-substituted aryls (e.g. methoxyphenyl,-

ethoxyphenyl, propoxypheny], butoxyphenyl, etc.), etc.

The pharmaceutically acceptable salts of the present compounds include addition salts with an inorganic acid such as hydrochloric acidysulfuric acid, nitric acid, phosphoric acid etc., and with organic acid such as oxalic. acid, maleic acid, malic acid, tartaric acid, methane-sulfonic acid, ethanesulfonic acid, etc.

Typical compounds represented by the general formula [l] are exemplified below: 1. 3-[4-(Ethoxycarbonyl-l l -dimethyl-methoxy)phenyl]--(3-pyridyl)-1,2,4-oxadiazole 2. 3-[4-(Ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl]- 5-(4-pyridyl)-l ,2,4-oxadiazole 3. 3-[4-(Ethoxycarbonyl-l ,l-dimethyl-methoxy)phenyl]-5-methyl-l ,2,4-oxadiazole 4. 3-[4-( Ethoxycarbonyl-l ,1-dimethyl-methoxy)phenyll-5-isopropyl-1 ,2,4-oxadiazole 5 3-[4-(Ethoxycarbonyl-l,1-dimethyl-methoxy)phenyl]-5-phenyl-l,2,4-oxadiazole 6. 3-[4-(Ethoxycarbonyl-1,l-dimethyl-methoxy)phenyl]-5-( 2-furyl)-l ,2,4-oxadiazole 7. 3-[4-( l-Ethoxycarbonyl-ethoxy )phenyl]-5-(3- pyridyl)-l ,2,4-oxadiazole 8. 3-[4-(Carboxyll l -dimethyl-methoxy )phenyl]-5- phenyl-l ,2,4-oxadiazole 9. 3-[4-( l-EthoxycarbonyI-butoxy,)phenyl]-5-( 3- pyridyl)-1 ,2,4-oxadiazole l0. 3-[ 4-(Carbamoyll ,l -dimethyl-methoxy)phenyl]- 5-( 3-pyridyl)-l ,2,4-oxadiazole l l. 3-[4-(Carboxyl-l l -dimethyl-methoxy)phenyl]-5-( 3-pyridyl)-I ,2,4-oxadiazole l2. 3-[4-(Buthoxycarbonyl-l l -dimethyl-methoxy)phenyl]-5-(3-pyridyl)-1,2,4-oxadiazole l3. 3-[4-(Benzyloxycarbonyl-l l -dimethyl-methoxy)phenyl]-5-( 3-pyridyl)-l ,2,4-oxadiazole l4. 3-[4-( Ethoxycarbonyll l -dimethyl-methoxy)phenyl ]-5-(2-chlorophenyl)-l ,2,4-oxadiazole l5 3-[4-(Ethoxycarbonyl-1 ,1 -dimethyl-methoxy)phenyl]-5-( 3-nitrophenyl)-l ,2,4-oxadiazole l6. 3-[ 4-( Ethoxycarbonyll l -dimethyl-methoxy)phenyl]-5- (2-thienyl)-l ,2,4-oxadiazole l7. 3-[ 4-(Ethoxycarbonyl-l l -dimethyl-methoxy)phenyl ]-5-heptyl- 1 ,2,4-oxadiazole l 8.- 3-[4-(Ethoxycarbonyll ,1 -dimethyl-methoxy)phenyl]-5-cyclohexylmethyl-l ,2,4-oxadiazole l9. 3-[4-( l-Ethoxycarbonyl-nonyloxy )phenyl]-5-(3- pyridyl)-l ,2,4-oxadiazole 20. 3-[4-(Ethoxycarbonyl-l-phenyl-methoxy)phenyl]- 5-( 3-pyridyl l ,2,4-oxadiazole I 2 l. 3-[4-( Ethoxycarbonyll -cyclohexyl-methoxy)phenyl]-5-(3-pyridyl)-1,2,4-oxadiazole The present compounds of the general formula [I] are prepared by the reaction of a compound of the general formula [ll] [wherein R R and X have same meaning as above] with a carboxylic-acid of the general formula [III] R COOH [Ill] [wherein R has the same meaning as above] or its acid halide, acid anhydride or ester.

The acid halide of the compound [III] includes, for instance, the corresponding acid chloride, acid'bromide, etc. The corresponding ester includes, for instance, alkyl esters (e.g. methyl, ethyl, propyl, butyl ester, etc.), aryl esters (e.g. phenyl, tolyl ester, etc.), etc.

The acid anhydride may be that prepared by condensation of two moles of the compound [III] or a socalled mixed acid anhydride prepared by condensation of 1 mole part of a suitable organic acid (e.g. acetic acid, propionic acid, butyric acid, benzoic acid, caproic acid, capric acid, caprylic acid, myristic acid, etc.) and 1 mole part of the compound [Ill].

An amount of the compound [III] or its derivative to be used for the reaction is usually about 1.2 to 1.5 moles per mole of the compound [II]. The reaction conditions may vary according to the kind of the starting compounds or other factors.

When the compound [llI].itself or its acid anhydride or ester is used as one of the starting materials, the reaction is usually carried out in the absence of a solvent under heating at about C or higher, more preferably at about 100 to about C, but a suitable solvent (e.g. dioxane, toluene, benzene) may occasionally be used. A basic substance may also be used. The basic substance is exemplified by alkali metal hydroxides (e.g. sodium hydroxide, potassium hydroxide etc.), and alkali metal carbonates (e.g. sodium carbonate, potassium carbonate, etc.).

When an acid halide corresponding to the compound [III] is used, the reaction is carried out preferably in the presence of an acid acceptor atroom temperature or under heating at about 150C or lower.

The acid acceptor usable is exemplified by organic amines such as pyridine, picoline, and triethylamine.

When the organic amine is used in a large amount, it can act also as a reaction solvent. Other suitable inert solvent such as dioxane, toluene, benzene may also be used. The reaction time is generally about 30 minutes to several hours.

After completion of the reaction, the objective compounds of the general formula [I] may be isolated and purified by conventional manners, e.g. extraction with a suitable solvent (e.g. ethyl acetate, chloroform, etc.), followed by evaporation, recrystallization, columnchromatography, etc.

When the radical represented by the symbol R is heterocyclic group containing one or more nitrogen atom(s) or a hydrocarbon group having one or more amino group(s) as substituent(s), the objective compounds may be converted to its addition salts with the afore-mentioned inorganic or organic acid after a conventional manner. Further, when the radical X is COOH, the resultant may be converted to a salt with a basic compound such as inorganic alkalis (e.g. sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc.) and organic. amines (e.g. pyridine, aniline, 2-hydroxyethylamine, etc.), etc.

pounds and may be prepared by the step described in the following scheme:

[wherein R R and X have the same meaning as above].

This reaction is usually carried out in a suitable solvent under heating at about 70 to about 80C. The solvent may be a mixture of water and a suitable organic solvent (e.g. methyl alcohol, ethyl alcohol, acetone, etc.).

The objective compounds of the general formula [I] have unique and characteristic pharmacological properties mentioned below:

1. The compounds [I] have a strong action of lowering the cholesterol level in a living body, particularly in a liver.

2. They can effectively restrain the synthesis of cholesterol in a living body, such as in liver, without production of undesirable steroids (e.g. desmosterol, etc.).

3. They prevent the accumulation of cholesterol in a living body, particularly in the liver and arota.

4. They show very low toxicity to mammals.

Taking advantage of the above characteristic properties, the objective compounds of the present invention can be used as a hypocholesterolemic agent and/or a medicine for improvingor preventing atherosclerosis. These compounds are administered for this purpose in per se or in form of a pharmaceutically acceptable composition in admixture with a suitable and conventional carrier or adjuvant.

The pharmaceutical composition may take the form of tablets, granules, powders, capsules and may be administered orally or parenterally.

Usual daily doses of the present compounds lie in the range of about 50 mg. to about 1,500 mg. per human adult upon oral administration or injectional administration (e.g. intravenously, intramuscularly, etc.).

For further explanation of the present invention, the following Reference and Examples are given, wherein the word part(s) and (percent) are based on weight unless otherwise noted, and the relation between part and volume part corresponds to that between gram and milliliter.

Reference preparation of the starting compound-- In 250 volume parts ofa mixture of ethyl alcohol and water (3:2) is dissolved 48 parts of 4-(ethoxycarbonyl- 1, l -dimethyl-methoxy)benzonitrile, and to the solution are added 18.2 parts of hydroxylamine hydrochloride and 13.8 parts of anhydrous sodium carbonate. The whole mixture is heated at 70 to 80C for 3 hours.

The resultant is concentrated under reduced pressure. The residue is extracted with ethyl acetate and the ethyl acetate layer is extracted with 150 volume parts of 10 weight percent hydrochloric acid.

The acid portion is alkalified with a 10 percent aqueous solution of sodium hydroxide and the separated oily substance is extracted with ethyl acetate. The organic layer is washed with water, dried over anhydrous sodium sulfate and then subjected to distillation under reduced pressure to leave 20.5 parts of 4-(ethoxycarbonyl-l ,1 -dimethyl-methoxy)benzamidoxime melting at 1 17 to 119C.

Analysis: Calculated for C, H, O N

Found:

After a similar manner to the above, the following compounds are prepared: 4-( 1-Ethoxycarbonyl-ethoxy)benzamidoxime melting at 120 to 122C 4-( 1-Ethoxycarbonyl-pentoxy)benzamidoxime melting at 62 to 64C 4-( 1-Ethoxycarbonyl-nonyloxy)benzamidoxime melting at to 76C 4-( Ethoxycarbonyl-phenyl-methoxy )benzamidoxim e melting at 133 to 134C 4-( Ethoxycarbonyll -cyclohexyl-methoxy)benzamidoxime melting at 109 to l 10C EXAMPLE 1 To a solution of 4.2 parts of nicotinic acid chloride in 20 volume parts of pyridine is added 4.0 parts of 4- (ethoxycarbonyl- 1 l -dimethyl-methoxy)benzamidoxime, and the whole mixture is refluxed for 2.5 hours.

The reaction mixture is concentrated under reduced pressure and the oily residue is dissolved in 200 volume parts of a saturated aqueous solution of sodium bicarbonate. The separated oily substance is extracted with ethyl acetate and the ethyl acetate layer is dried over anhydrous sodium sulfate, followed by concentration under reduced pressure.

I The oily residue is treated with oxalic acid and the separated crystals are recrystallized from ethyl alcohol. This procedure gives 2.1 parts of 3-[4-(ethoxycarbonyl-l ,1-dimethyl-methoxy)phenyl]-5-(3-pyridyl)-1,2,4- oxadizole oxalate as colorless needles melting at 129 to 131C. Yield: 35.1 percent Analysis: Calculated for C H N O %C H O C,60.30; H,S.18; N,10.79 Found: C,60.36; H,4.92; N,l0.55

EXAMPLE 2 To a solution of 2.0 parts of 4-(ethoxycarbonly-l ,1- dimethyl-methoxy)benzamidoxime in 10 volume parts of pyridine is added 2.1 parts of isonicotinic acid chloride, and the whole mixture is refluxed for 2.5 hours.

The reaction mixture is poured into 200 volume parts of ice water and the whole mixture is alkalified with a 10 percent aqueous solution of sodium hydroxide. The separated crystals are dissolved in ethyl ether. The solution is treated with oxalic acid and the separated crystals are recrystallized from methyl alcohol.

This procedure gives 1.5 parts of 3-[4-(ethoxycarbonyl-l l -dimethyl-methoxy)phenyl]-5-(4-pyridyl)- 1,2,4-oxadiazole oxalate as colorless fine needles melting at 131 to 133C. Yield: 50.3 percent Analysis: Calculated for C H, N O %C H O;,:

c 60.30; H, 5.18, N, 10.79 Found c 60.09; H, 4.97; N. 10.51

EXAMPLE 3 A solution of 2.0 parts of 4-(ethoxycarbonyl -1,ldimethyl-methoxy)benzamidoxime in 10 volume parts of isopropionic acid anhydride is heated at 140C for 2.5 hours and the reaction mixture is poured into 100 volume parts of water. The whole mixture is alkalified with a 10 percent aqueous solution of sodium hydroxide and the separated oily substance is extracted with ethyl acetate. The ethyl acetate layer is washed with water, dried over anhydrous sodium sulfate, and then concentrated under reduced pressure. The residue is treated with silica-gel column-chromatography to give 2.1 parts of 3-[4-(ethoxycarbonyl-l,1-dimethylmethoxy)phenyl]-5-isopropyl-1,2,4-oxadiazole as a colorless oily substance. Yield: 88.9 percent.

Analysis: Calculated for C I-1 N C 64.13, H 6.9 0 Found: C 64.37, H 6.91, 8

Nuclear Magnetic Resonance spectrum (1') (in CDC1 2.03 (2H, d. J=l c.p.s. aromatic H of 3-phenyl) 3.10 (2H, d. J=15 c.p.s. aromatic H of 3-phenyl). 5.78 (21-1, q. J=12 c.p.s, Cl-l CH A solution of 2.0 parts of 4-(ethoxycarbonyl-l,ldimethyl-methoxy)benzamidoxime in 5 volume parts of benzoyl chloride is heated at 130 to 140C for 3 hours and then the reaction mixture is poured into 100 volume parts of ice water. The whole mixture is alkalified with a percent aqueous solution of sodium hydroxide and the separated oily substance is extracted with chloroform. The chloro-form layer is washed with water, dried and then concentrated under reduced pressure.

The residue is treated with silica-gel column-chromatography to give 1.6 parts 3-[4-(ethoxycarbonyl- 1 ,1-dimethyl-methoxy)phenyl]-5-phenyl-l ,2,4-oxadiazole as a colorless oily substance. Yield: 51.2 percent Analysis: Calculated for C H N O C 8.17, H5.79. N7.95 Found: C 67.92. H 5.78, N 7.45

1.94 (2H, d., J=l5 c.p.s., aromatic H of 3-phenyl). 2.40 to 2.66 (5H, m. aromatic H of S-phenyl). 3.06 (2H, d., J=l 5 c.p.s., aromatic H of 3-phenyl). 5.48 (2H, q., J=l2 c.p.s., -O--CH EXAMPLE 5 A solution of 2.5 parts of 4-(ethoxycarbonyl-l ,1- dimethyl-methoxy)benzamidoxime and 1.8 parts of furoyl chloride in 5 volume parts of pyridine is heated at 130 to 140C for 2.5 hours, and the reaction mixture is poured into volume parts of ice water.

. The separated oily substance is extracted with ethyl acetate and the ethyl acetate .layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure to remove ethyl EXAMPLE6 A solution of 1.5 parts of 4-(l-ethoxycarbonylethoxy)benzamidoxime and 1.6 parts of nicotinic acid.

chloride in 7 volume parts of pyridine is refluxed for 3.5 hours. The reaction mixture is poured into 75 volume partsof ice water and the whole mixture is alkalified with a 10 percent aqueous solution of sodium hydroxide. The separated oily substance is extracted with chloroform and the chloroform layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure to remove the chloroform. The residue is treated with silica-gel column-chromatography to give 0.8 part of 3-[4-(1- ethoxycarbonyl-ethoxy)pheny1]-5-( 3-pyridyl)-1 ,2,4- oxadiazole as pale red flakes melting at 103 to 105C. Yield: 39.7 percent Analysis: Calculated for C H,-,O.,N

EXAMPLE 7 chloroform layer is washed with a 10 percent aqueous solution of sodium hydroxide, water, a 10 percent hydrochloric acid and water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave a pale yellowbrown oily substance. The oily substance is treated with silica-gel column-chromatography to give 1.0 part of 3- [4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl]-5- [4-(t-butyl)phenyl-]-1,2,4-oxadiazole as colorless needles melting at 69 to 70C. Yield: 65.0 percent.

Analysis: Calculated for C I-1 N c 70.56, H 6.91, N 6.86 Found c 70.67, H 6.79, N. 6.42

EXAMPLE 8 To a solution of 1.0 part of 4-(ethoxyca'rbonyl-1,ldimethyl-methoxy)benzamidoxime in 5 volume parts of pyridine is added 1.4 parts of 4-nitrobenzoyl chloride, and the whole mixture is refluxed for 2 hours. The reaction mixture is poured into 50 volume parts of ice water and the separated oily substance is extracted with 50 volume parts of chloroform.

The chloroform layer is washed with a percent aqueous solution of sodium hydroxide, water, a 10 percent hydrochloric acid and water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave 1.8 parts of yellow crystals.

The crystals are recrystallized from a mixture of benzene and petroleum benzine to give 1.1 parts of 3- [4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyll-S- (4-nitrophenyl)-1,2,4-oxadiazole as yellow needles melting at 91C. Yield: 73.5 percent.

Analysis: Calculated for C l-1 N O c 60.45, H 4.82, N 10.58 Found: c 60.53, H 4.83, N 10.33

EXAMPLE 9 To a solution of 1.0 part of 4-(ethoxycarbonyl-l,1- dimethyl-methoxy)benzamidoxime in 5 volume parts of pyridine is added 1.4 parts of 3-nitrobenzoyl chloride, and the whole mixture is refluxed for 2 hours.

The reaction mixture is poured into 50 volume parts of ice water and the whole mixture is subjected to extraction with 50 volume parts of chloroform. The chloroform layer is washed with a 10 percent aqueous solution of sodium hydroxide, water, a 10 percent hydrochloric acid and water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave 1.5 parts of pale yellow crystals.

The crystals are recrystallized from a mixture of benzene and petroleum benzine to give 1.1 parts of 3- [4-(ethoxycarbonyl-l ,1-dimethyl-methoxy)phenyl]-5- (3-nitrophenyl)-1,2,4-oxadiazole as pale yellow needles melting at 1 12 to 1 14C. Yield: 73.7 percent Analysis: Calculated for C l-l N O C 60.45, H 4.82, N 10.58 Found: c 60.48, H 4.77, N 10.37

EXAMPLE 10 To a solution of 1.0 part of 4-(ethoxycarbonyl-l,ldimethyl-methoxy)benzamidoxime in 5 volume parts of pyridine is added 0.9 part of 2-chlorobenzoyl chloride, and the whole mixture is heated at 120 to 130C for 3.5 hours. I

The reaction mixture is poured into 50 volume parts of ice water and the separated oily substance is extracted with 50 volume parts of chloroform. The chloroform layer is washed with a 10 percent aqueous solution of sodium hydroxide, water, a 10 percent hydrochloric acid, and water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave 1.7 parts of an oily substance.

The oily substance is treated with silica-gel columnchromatography to give 1.0 part of 3-[4-(ethoxycarbonyl-l ,1-dimethyl-methoxy)phenyl]-5-( 2- chlorophenyl)-1,2,4-oxadiazole as a pale yellow-brown oily substance. Yield: 69.0 percent Analysis: Calculated for C H N O Cl:

1-1 4.95, N 7.24 Found: H 4.87, N 6.85

Nuclear Magnetic Resonance spectrum (1') (in 1.91 (2H, d. J=15 c.p.s., aromatic H of 3-phenyl) 2.44 to 2.73 (3H, m, aromatic H of 3'-phenyl) 3.05 (2H, d. J=l 5 c.p.s. aromatic H of 3-phenyl) EXAMPLE 1 1 To a solution of 1.0 part of 4-(ethoxycarbonyl-l ,1- dimethyl-methoxy)benzamidoximime in 5 volume parts of pyridine is added 0.99 partof 3-chlorobenzoyl chloride, and the whole mixture is refluxed for 3.5 hours.

The reaction mixture is poured into 50 volume parts of ice water, and the separated oily substance is extracted with 50 volume parts of chloroform.

The chloroform layer is washed with a 10 percent aqueous solution of sodium hydroxide, water, a 10 percent hydrochloric acid and water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave 1.6 parts of a brown oily substance. The oily substance is treated with silica-gel column-chromatography to give 1.3 parts of 3-[4-(ethoxy-carbonyl- 1,1-dimethyl-methoxy)phenyl]-5-(3-chlorophenyl)1,2,4-oxadiazole. Yield: 89.6 percent Analysis: Calculated for C l-l N O Cl Found:

Nuclear Magnetic Resonance spectrum ('r) (in CDCl 1.78 to 2.00 (2H, m. aromatic H of S-phenyl) 1.96 (21-1, d. J=15 c.p.s., aromatic H of 3-phenyl) 2.48 to 2.58 1H, m. aromatic H of S-phenyl) 2.68 (1H, s. aromatic H of S-phenyl) 3.07 (21-1, d. J=l5 c.p.s., aromatic H of 3-phenyl) 5.77 (2H, q. J=l2 c.p.s., OCH

EXAMPLE 12 To a solution of 1.0 part of 4-(ethoxycarbonyl-l,ldimethyl-methoxy)benzamidoxime in 5 volume parts of pyridine is added 0.99 part of 4-chlorobenzoyl chloride, and the whole mixture is refluxed for 2 hours. The reaction mixture is poured into 50 volume parts of ice water and the separated crystals are extracted with chloroform. The chloroform layer is washed with a 10 percent aqueous solution of sodium hydroxide, water, a 10 percent hydrochloric acid, and water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave 1.8 parts of pale red crystals. The crystals are recrystallized from petroleumbenzine to give 0.9 part of 3-[4- (e'thoxycarbonyl-l l -dimethyl-methoxy)-phenyl]-5-(4-.

chlorophenyl)-1,2,4'oxadiazole as pale red needles melting at 93 to 94C. Yield: 62.0 percent Analysis: Calculated for C H N- O Cl:

62.09, 114.95, N724, c19.17 62.35, 114.93; N724, Cl9.16

EXAMPLE 13 To a solution of 1.0 part of 4-(ethoxycarbonyl-1,1- dimethyl-methoxy)benzamidoxime in 5 volume parts of pyridine is added 0.96 part of 2-methoxybenzoyl chloride, and the whole mixture is refluxed for 3.5 hours. The reaction mixture is poured into 50 volume parts of ice water and the whole mixture is subjected to extraction with 100 volume parts of chloroform. The chloroform layer is washed with a 10 percent aqueous solution of sodium hydroxide,- water, a 10 percent hydrochloric acidand'water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave 1.7 parts of a colorless oily substance. The oily substance is treated with silica-gel. column-chromatography to yield 1.0 part of 3-[4-(ethoxycarbonyl-l 1 -dimethyl-methoxy)phenyl]-5-(2-methoxyphenyl)-1,2,4-oxadiazole colorless plates melting at 79 to 80C. Yield: 69.0 percent Analysis: Calculated for C I-1 N c 65.95, 11 5.80, N 7.33 Found c 65.67, 11 5.78, N 6.84

EXAMPLE :14

To a solution of 1.0 part of -4-(ethoxycarbonyl-l,1- dimethyl-methoxy)benzamidoxime in volume parts of pyridine is added 0.96 part of 4-methoxybenzoyl chloride, and the whole mixture is refluxed for 3 hours. The reaction mixture is poured into 50 volume parts of ice water and the separated oily substance is extracted with 100 volume partsof chloroform. The chloroform layer is washed with a percent aqueous solution of sodium hydroxide, water, a 10 percent hydrochloric acid and water in this order, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave 1.5 parts of colorless crystals. The crystals are recrystallized from methyl alcohol to give 0.9 part of 3-[4-(ethoxycarbonyl-l,l-dimethylmethoxy)-phenyl]-5-(4-methoxyphenyl)-1,2,4-oxadiazole as colorless needles melting at 83 to 85C. Yield: 62.6 percent -12... Analysis: Calculated for C ,H N O,:

c 65.95, 11 5,80, N 7.33 Found: c 66.04, 115,89, N 7.05

EXAMPLE 15 To a solution of 1.0 part of 4-(ethoxycarbonyl-l ,1- dimethyl-methoxy)benzamidoxime in 5 volume parts of pyridine is added 0.91 part of 4-aminobenzoyl chloride, and the whole mixture is refluxed for 2 hours. The reaction mixture is concentrated under reduced pressure. To the residue is added 10 volumeparts of a 10 percent aqueous solution of sodium hydroxide and the whole mixture is subjected to extraction with50 volume parts of chloroform.

The chloroform layer is washed with water, dried and concentrated to dryness. This procedure gives a brown oily substance.

The oily substance is treated with silica-gel columnchromatography to give 1.3 parts of 3-[4-(ethoxy-carbonyl-l ,1 -dimethyl-methoxy)pheny1]-5-(4- aminophenyl)-1,2,4-oxadiazole as pale brown short needles melting at 109 to l 1 1C. Yield: 92.4 percent.

7 Analysis: Calculated for C H N O c 65.38, 11 5.76, N 11.44 Found: c 65.02, 11 5.65, N 11.71

EXAMPLE 16 To a solution of 2.0 parts of 4-(ethoxycarbonyl-l ,ldimethyl-methoxy)benzamidoxime in 10 volume parts of pyridine is added 1.82 parts of 3-aminobenzoyl chloride, and the whole mixture is refluxed for 2 hours. The reaction mixture is concentrated under reduced pressure, and to the residue is added 20 volume parts of a 10 percent aqueous solution of sodium hydroxide. The whole mixture is subjected to extraction with 50 volume parts of chloroform and the chloroform layer is washed with water, followed by drying. The chloroform layer is then subjected to distillation under reduced pressure to leave a brown oily substance. The oily substance is treated with silica-gel column-chromatography to give 1.3 parts of 3-[4-(ethoxycarbonyl-l,1- dimethyl-methoxy)phenyl]-5-( 3-aminophenyl)-l ,2,4- oxadiazole as a pale brown oily substance. Yield: 54.4 percent.

Analysis: Calculated for C H N O c 65.3 .7 N 11.4 Found; (365-4 .9 Nl1.0

spectrum (7) (in EXAMPLE 17 A solution of 1.3 parts of 4-(ethoxycarbonyl-l,ldimethyl-methoxy)benzamidoxime and 1.7 parts of 2- thienoyl chloride in a mixture of 2 volume parts of triethylamine and 10 volume parts of dioxane is heated at 120 to 130C for 4 hours, and the reaction mixture is poured into 100 volume parts of ice water.

The separated oily substance is extracted with ethyl acetate and the organic layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced'pressure. The residue is treated with silica-gel column-chromatography to give 1.5 parts of 3-[4-ethoxycarbonyl- 1 1 -dimethy1-methoxy)phenyl]--(2-thienyl)-l,2,4-oxadiazole as colorless needles melting at 89 to 91C. Yield: 85.7 percent.

Analysis: Calculated for C H N O S A solution of 1.3 parts of 4-(ethoxycarbonyl-l,l-

dimethyl-methoxy)benzamidoxime and 1.9 parts of phenyl-acetyl chloride in a mixture of 2 volume parts of triethylamine and volume parts of dioxane is heated at 120 to 130C for 4 hours and the reaction mixture is poured into 100 volume parts of ice water.

The separated oily substance is extracted with ethyl acetate and the organic layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure. The residue is treated with silica-gel column-chromatography to give 1.6 parts of 3-[4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl]-5-benzyl-l ,2,4-oxadiazole as a pale yellow oily substance. Yield: 89.5 percent Analysis: Calculated for C H N O Nuclear Magnetic Resonance spectrum ('7) (in CDCl 2.02 (2H, d. J=l 5 c.p.s. aromatic H of 3-phenyl) 2.67 (5H, s. aromatic H of benzyl) 3.10 (2H, d. J= c.p.s. aromatic H of 3-phenyl) 5.80 (2H, q. J=l2 c.p.s. CH -CH 8.80 (3H, t. J=l2 c.p.s. -CH CH EXAMPLE 19 A solution of 1.3 parts of 4-(ethoxycarbonyl-l,ldimethyl-methoxy)benzamidoxime and 2.0 parts of cyclohexylacetyl chloride in a mixture of 2 volume parts of triethylamine and 10 volume parts of dioxane is heated at 130 to 140C for 5 hours, and the reaction mixture is poured into 100 volume parts of ice water.

Found: C 67.45, H 7.56,

Nuclear Magnetic Resonance spectrum (7') (in CDCl;,). 2.02 (2H, d. J=l5 c.p.s. aromatic'H of 3-phenyl) 3.09 (2H, d. J=l 5 c.p.s. aromatic H of 3-phenyl) 5.76 (2H, q. J=l2 c.p.s. -OCH CH 8.02 to 8.90 l 1H, m. H of cyclohexyl).

8.80 (3H, t. J=l2 c.p.s. CH CH EXAMPLE 20 A solution of 1.3 parts of 4(ethoxycarbonyl-l ,1- dimethyl-methoxy)benzamidoxime and 2.0 parts of octanoyl chloride in a mixture of 2 volume parts of triethylamine and 10 volume parts of dioxane is heated at to C for 5 hours and the reaction mixture is poured into 100 volume parts of ice water. The separated oily substance is extracted with ethyl acetate, and the organic layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure. The residue is treated with silica-gel column chromatography to give 1.7 parts of 3- [4-(ethoxycarbonyl-1,l-dimethyl-methoxy)phenyl]-5- heptyl-l ,2,4-oxadiazole as a pale yellow oily substance. Yield: 93 .0 percent.

Analysis: Calculated for C H N O Found:

Nuclear Magnetic Resonance spectrum (1') (in CDCl 2.03 (2H, cl. J=l5 c.p.s. aromatic H of 3-phenyl) 3.09 (2H, d. J=l5 c.p.s. aromatic H of 3-phenyl) 5.77 (2H, q. J=l2 c.p.s. -O-CH -CH 7.08 (2H, J=13 c.p.s. ll I A solution of 1.3 parts of 4-(ethoxycarbonyl-1,land 2.7 parts of palmitic anhydride in. 10 volume parts of dioxaneis heated at 130 to 140C for 5 hours, and the reaction mixture is poured into 100 volume parts'of ice water. The separated oily substance is extracted with ethyl acetate and the organic layer is washed with a percent aqueous solution of sodium hydroxide, and then water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure. The residue is treated with silica-gel column-chromatography to give 1.5 parts of 3-[4-(ethoxycarbonyl-l,1- dimethyl-methoxy)phenyl]-5-pentadecyl-'1,2,4-oxadiazole as colorless needles melting at .35 to 37 C. Yield: 73.3 percent Analysis: Calculated for C H N O c 71.57, H 9.53, N 5.76 Found: C 71.56, H 9.86, N 5.69

EXAMPLE 22 1.3 parts of volume parts of triethylamine and 10 volume parts of dioxane is heated at 120 to 130C for 2 hours, and the reaction mixture is poured into 100 volume parts of ice water.

The separated oily substance is extracted with ethyl acetate and, the organic layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure. The residue is treated with silica-gel column-chromatography to give 1.7 parts of 3-[4-( l-ethoxycarbonyl-l-phenyl-methoxy)phenyl]-5-(3-pyridyl)-l,2,4-oxadiazole as colorless needles melting at 89 to 91C. Yield: 66.6 percent.

Analysis: Calculated for C H N O c 68.81, H 4.77, N 10.47 Found: c 68.47, 11 4.65, N 10.18

EXAMPLE 23 ,oilysubstance. Yield: 42.9 percent.

Analysis: Calculated for C i-1 N 0 Found:

Nuclear. Magnetic Resonance spectrum h) (in CDCl,)

0.60 (1H, d. J=3 c.p.s. aromatic H of S-pyridyl) 1.20 (1H, q. J=9 c.p.s., J=3 c.p.s. aromatic H of 5- pyridyl).

1.58 (1H, Se. J=9 c.p.s., J=3 c.p.s. aromatic H of S-pyridyl).

1.93 (2H, d. J=15 c.p.s. aromatic H of 3-pheny1) 2.54 (1H, q. J=15 c.p.s., J=9 c.p.s. aromatic H of S-pyridyl) 3.01 (2H, d. J=15 c.p.s. aromatic H of 3-pheny1) 5.77 21-1, q. J=12 c.p.s. O-CH,CH3).

8.64 to 9.22 (18 H, m. -OCH,-Cl-l cH EXAMPLE 24 A solution of 3.0 parts of 4-(1-ethoxycarbonyl-lcyclohexyl-methoxy)benzamidoxime and 2.0 parts of nicotinoyl chloride hydrochloride in a mixture of 2 volume parts of triethylamine and 20 volume parts of dioxane is heated at to C for 2 hours.

The reaction mixture is poured into 200 volume parts of ice water. The separated oily substance is extracted with ethyl acetate and the organic-layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure. The residue is treated with silica-gel column-chromatography to give 1.0 part of 3-[4-(1-ethoxycarbonyll-cyclohexyl-methoxy)-phenyl]-5-( 3-pyridyl)-1 ,2,4- oxadiazole as colorless needles. melting at 105 to 107C. Yield: 24.2 percent Analysis Calculated for C H N O c 67.79, 11 6.18, N 10.31 Found: c 67.46, H 6.08, N 10.42

EXAMPLE 25 A solution of 3.0 parts of 4-( l-ethoxycarbonyl-pentyloxy)benzamidoxime and 2.7 parts of nicotinoyl chloride hydrochloride in 15 volume parts of pyridine is heated at 130 to C for 2 hours, and the reaction mixture is poured into volume parts of ice water. The separated oily substance is extracted with chloroform and the organic layer is washed with water, dried over anhydrous sodium sulfate, followed by distillation under reduced pressure. The residue is treated with silica-gel column-chromatography to give 2.7 parts of 3-[4-( 1-ethoxycarbonyl-pentyloxy)phenyl] -5- (3-pyridy1)-1,2,4-oxadiazo1e as a pale brown oily substance. Yield: 69.5 percent.

Analysis: Calculated for C l-1 N 0 Found:

Nuclear Magnetic Resonance spectrum r) (in CDCl 0.60 1H, d. J=3 c.p.s. aromatic H of S-pyridyl).

1.19 (1H, q. J=9 c.p.s., J=3 c.p.s. aromatic H of 5- pyridyl). 1.58 (1H. Se. J= c.p.s., J=3 c.p.s. aromatic H of S-pyridyl).

1.93 (1H, d. J=l5 c.p.s. aromatic H of 3-pheny1) 2.54 (1H, q. J=15 c.p.s. J=9 c.p.s. aromatic H of 5- py y 3.02 (2H, d. J=l 5 c.p.s. aromatic H of 3-phenyl) 5.78 (211, q. J=12 c.p.s. OCH CH 7.90 to 9.20 (12H, m. -OCH -CH (CH After a similar manner to the above examples, the following compounds are prepared: 3-[4-(Benzy1oxycarbonyll ,1-dimethy1-methoxy)pheny1]-5-(3-pyridy1)-1,2,4-oxadiazole melting at 72 to 73C 3-[4-(Carbamoyl-l l -dimethyl-methoxy)phenyl]-5-(3- pyridy1)-l ,2,4-oxadiazole melting at 174 to 175C 3-[4-(Butoxycarbonyl-1,1-dimethyl-methoxy)phenyll- 5-(3-pyridy1)- l ,2,4-oxadiazole melting at 82 to 84C 3-[4-(Carboxy-l,1-dimethyl-methoxy)phenyl]-5-(3- pyridy1)-1,2,4-oxadiaz0le melting at 195 to 197C.

What we claim is:

1. A compound of the general formula wherein X represents carboxyl, carbo-lower alkoxy or carbamoyl, each of R and R represents a hydrogen atom, carbobenzyloxy, lower alkyl group or one of said terms represents cyclohexyl, or phenyl; R is a number selected from the group consisting of alkyl having one to four carbon atoms, linear alkyl having from five to 17 carbon atoms, cyclohexyl, cyclohe'xylmethyl, benzyl, phenethyl, phenyl, lower-alkylphenyl, lower-alkoxyphenyl, halophenyl, aminophenyl, nitrophenyl, pyridyl, furyl, or theinyl or its pharmaceutically acceptable salts.

2. A compound as claimed in claim 1, wherein R is a linear alkyl group having five to seven carbon atoms.

3. A compound as claimed in claim 1, wherein R is a linear alkyl group having 15 to 17 carbon atoms.

4. A compound as claimed in claim 1, wherein R is phenyl which may be substituted.

5. A compound as claimed in claim 1, wherein R is phenethyl group which may be substituted.

6. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l 1 -dimethylmethoxy)-phenyl]-5-(3-pyridyl)-1,2,4-oxadiazole.

7. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l,1-dimethylmethoxy )pheny11-5 -(4-pyridyl)- l ,2,4-oxadiazole.

8. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-1,1-dimethylmethoxy)phenyl]-5-isopropy1-1,2,4-oxadiazole.

9. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyll l-dimethylmethoxy)-phenyl]-5-pheny1- l ,2,4-oxadiazole.

10. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyll l -dimethylmethoxy)-phenyl]-5-( 2-furyl)- l ,2,4-oxadiazole.

11. A compound as claimed in claim 1, wherein the compound is 3-[4-(1-ethoxycarbonyl-ethoxy)phenyl]- 5-( 3-pyridyl)- 1 ,2,4-oxadiazo1e.

12. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l l -dimethylmethoxy)-phenyl)-5-[4-(t-buty1)phenyl]-l ,2,4-oxadiazole.

13. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyll l -dimet hylmethoxy)-pheny1]-5-(4-nitropheny1)- l ,2,4-oxadiazole.

14. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl- 1 ,1 -dimethylmethoxy)-phenyl]-5-(3-nitrophenyl)-1,2,4-oxadiazole.

15. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-1 1 -dimeth ylmethoxy)-phenyl] -5-( 2-chlorophenyl)-1 ,2,4-oxadiazole.

16. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l 1 -dimethylmethoxy)-phenyl]-5-(3-chlorophenyl)-1,2,4-oxadiazole.

17. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-1 l -dimethy1- methoxy)-phenyl]-5-(4-chlorophenyl)-1,2,4-oxadiazole.

18. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l 1 -dimethy1- methoxy)-phenyl]-5-( 2-methoxypheny1)-l ,2,4-oxadiazole.

19. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l l -dimethylmethoxy)-phenyl]-5-(4-methoxypheny1)- 1 ,2,4-0xadiazole.

20. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l l -dimethylmethoxy)-phenyl]-5-(4-aminophenyl)-l ,2,4-oxadiazole.

21. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyll l -dimethylmeth'oxy)-phenyl]-5-( 3-aminophenyl)- l ,2,4-oxadiazole.

22. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l 1 -dimethylmethoxy)-pheny1]-5-( 2-thienyl)-l ,2,4-oxadiazole.

23. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l,l-dimethylmethoxy)-phenyl] -5-benzyl-1 ,2,4-oxadiazole.

24. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l,l-dimethylmethoxy)phenyl]-5-(cyc1ohexyl-methyl)-1,2,4-oxadiazole.

25. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbonyl-l ,l-dimethylmethoxy)phenyl]-5-hepty1-1,2,4-oxadiazo1e.

26. A compound as claimed in claim 1, wherein the compound is 3-[4-(ethoxycarbony1- l 1 -dimethylmethoxy)phenyl]-5-pentadecy1- l ,2,4-oxadiazo1e.

27. A compound as claimed in claim 1, wherein the compound is 3-[ 4-( l-ethoxycarbonyll -phenylmethoxy)phenyl]-5% 3-pyridy1)-1 ,2,4-oxadiazo1e.

methoxy)phenyl]-5-( 3-pyridyl)-l ,2,4-oxadiazole.

32. A compound as claimed in claim 1, wherein the compound is 3-[4-(carbamoyl-l,l-dimethyl-methoxy)phenyl]-5-( 3-pyridyl)-l ,2,4-oxadiazole.

33. A compound as claimed in claim 1, wherein the compound is 3-[4-(butoxycarbonyl-l l -dimethylmethoxy)phenyl]-5-(3-pyridyl-)-1 ,2,4-oxadiazole.

34. A compound as claimed in claim 1, wherein the compound is 3-[4-(carboxy-1,l-dimethyl-methoxy)phenyl]-5-( 3-pyridyl)-l ,2,4-oxadiazole.

* l I I t 

2. A compound as claimed in claim 1, wherein R3 is a linear alkyl group having five to seven carbon atoms.
 3. A compound as claimed in claim 1, wherein R3 is a linear alkyl group having 15 to 17 carbon atoms.
 4. A compound as claimed in claim 1, wherein R3 is phenyl which may be substituted.
 5. A compound as claimed in claim 1, wherein R3 is phenethyl group which may be substituted.
 6. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(3-pyridyl)-1, 2,4-oxadiazole.
 7. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl)-5-(4-pyridyl)-1, 2,4-oxadiazole.
 8. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl)-5-isopropyl-1,2, 4-oxadiazole.
 9. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-phenyl-1,2,4 -oxadiazole.
 10. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(2-furyl)-1,2, 4-oxadiazole.
 11. A compound as claimed in claim 1, wherein the compound is 3-(4-(1-ethoxycarbonyl-ethoxy)phenyl)-5-(3-pyridyl)-1,2,4-oxadiazole.
 12. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(4-(t-butyl)phenyl) -1,2,4-oxadiazole.
 13. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(4-nitrophenyl)-1,2,4 -oxadiazole.
 14. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(3-nitrophenyl)-1,2,4 -oxadiazole.
 15. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl) -5-(2-chlorophenyl)-1,2,4-oxadiazole.
 16. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(3-chlorophenyl)-1,2,4 -oxadiazole.
 17. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(4-chlorophenyl)-1,2,4 -oxadiazole.
 18. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(2-methoxyphenyl)-1,2,4-oxadiazole.
 19. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(4-methoxyphenyl)-1,2,4-oxadiazole.
 20. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(4-aminophenyl)-1,2,4 -oxadiazole.
 21. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(3-aminophenyl)-1,2,4 -oxadiazole.
 22. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-(2-thienyl)-1, 2,4-oxadiazole.
 23. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)-phenyl)-5-benzyl-1,2,4 -oxadiazole.
 24. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl)-5-(cyclohexyl-methyl) -1,2,4-oxadiazole.
 25. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl)-5-heptyl-1,2,4-oxadiazole.
 26. A compound as claimed in claim 1, wherein the compound is 3-(4-(ethoxycarbonyl-1,1-dimethyl-methoxy)phenyl)-5-pentadecyl-1,2, 4-oxadiazole.
 27. A compound as claimed in claim 1, wherein the compound is 3-(4-(1-ethoxycarbonyl-1-phenyl-methoxy)phenyl)-5-(3-pyridyl)-1,2, 4-oxadiazole.
 28. A compound as claimed in claim 1, wherein the compound is 3-(4-(1-ethoxycarbonyl-nonyloxy)phenyl)-5-(3-pyridyl)-1,2,4-oxadiazole.
 29. A compound as claimed in claim 1, wherein the compound is 3-(4-(1-ethoxycarbonyl-1-cyclohexyl-methoxy)phenyl)-5-(3-pyridyl)-1,2,4 -oxadiazole.
 30. A compound as claimed in claim 1, wherein the compound is 3-(4-(1-ethoxycarbonyl-pentyloxy)phenyl)-5-(3-pyridyl)-1,2,4-oxadiazole.
 31. A compound as claimed in claim 1, wherein the compound is 3-(4-(benzyloxycarbonyl-1,1-dimethyl-methoxy)phenyl)-5-(3-pyridyl)-1,2,4 -oxadiazole.
 32. A compound as claimed in claim 1, wherein the compound is 3-(4-(carbamoyl-1,1-dimethyl-methoxy)phenyl)-5-(3-pyridyl)-1,2,4-oxadiazole.
 33. A compound as claimed in claim 1, wherein the compound is 3-(4-(butoxycarbonyl-1,1-Dimethyl-methoxy)phenyl)-5-(3-pyridyl)-1, 2,4-oxadiazole.
 34. A compound as claimed in claim 1, wherein the compound is 3-(4-(carboxy-1,1-dimethyl-methoxy)phenyl)-5-(3-pyridyl)-1,2,4-oxadiazole. 